1. Field of the Invention
The present invention relates to an insulating composition used in a superconductive element.
2. Description of the Related Art
Recently, various researches on oxide superconductors have been performed by many research groups since a laminate state perovskite type oxide of Ba-La-Cu-O series was represented to be possible to have a nature of high critical temperature (Z. Phys. B Condensed Matter 64, 189-193 (1986) ). Particularly, a defect-perovskite type oxide super conductor having oxygen defects represented by Y-Ba-Cu-O series has been confirmed to have a high critical temperature of 90 K or more which is higher level than liquid nitrogen (Phys. Rev. Lett. Vol. 58, No. 9, 908-910).
Further, in 1988, a superconductive oxide of Bi-Sr-Ca-Cu-O series having a high critical temperature of 105 K was discovered (NIHON KEIZAI SHINBUN dated Jan. 22, 1988, etc.).
The superconductive oxide of Bi-Sr-Ca-Cu-O series is an excellent oxide superconductive material as compared with a superconductive oxide of Ba-La-Cu-O series or of Y-Ba-Cu-O series because it does not necessitate to use rare-earth elements of high cost and has high chemical stability against moisture as well as be high critical temperature.
Now, the superconductive elements using tunnel effect have been advanced to apply to digital devices such as logical elements, memory elements, etc. in computer because of its high speed operation and its low power consumption. Further, 4-bits multiplier, 3K gate array, etc. employing Nb/Aloxide/Nb junction, NbN/MgO/NbN junction, etc. have been manufactured in trial. Moreover, superconductive 3-terminal elements as superconductor - semiconductor element have been manufactured in trial. However, all these elements are composed of superconductor of low critical temperature and liquid helium is used as cooling medium. Therefore, they are not practical yet in problems of development of peripheral technology economic, etc.
Consequently, applications of oxide superconductor having a high critical temperature to the above mentioned superconductive elements have been discussed.
However, in case of making the above mentioned superconductive elements by oxide superconductor and insulating composition, a problem remain that electron levels are newly produced at the crystal interface between the oxide superconductive layer and the insulating composition, and electrons are trapped because of the poor alignment nature thereof, thereby injuring functions as a Josephson element. Therefore, predetermined characteristics are hardly obtained.
Moreover, Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 having the transition temperature of in the vicinity of 110 K and Bi.sub.2 Sr.sub.2 Ca.sub.1 Cu.sub.2 O.sub.8 having the transition temperature of in the vicinity of 80 K have been known as Bi series superconductors. However, a problem remains a synthesis of Bi.sub.2 Sr.sub.2 Ca.sub.2 Cu.sub.3 O.sub.10 having higher critical temperature is not easy. The reason is considered that the problem is based on a modulation structure existing in the b crystal axis direction of the Bi series superconductor or internal stresses which cause the modulation structure.